Precision production potting

ABSTRACT

A production process for equipping a rough casting with a plurality of highly accurate surfaces at precisely predetermined locations on the casting without machining the casting. The casting includes a plurality of laterally spaced holes and is placed on a tool which supports a plurality of mounting bosses in the holes of the casting. The tool locates the bosses generally coaxial with the holes so that annular spaces are provided between the exterior of the bosses and the walls of the holes, which spaces are then filled with a bonding agent to secure the bosses to the casting. The tool positions selected faces of the bosses in desired relation to each other, preferably parallel to a reference surface defined by the tool. The tool seals an end of each annular space to prevent the bonding agent from flowing from the space as the agent cures.

United States Patent [72] lnventors James E. Blum Pasadena, Calif.; Robert P. Johnson, Pontiac, Mich. [21 Appl. No. 680,830 [22] Filed Nov. 6, 1967 [45] Patented Apr. 20, 1971 [73] Assignee Bell & Howell Company Chicago, Ill.

[54] PRECISION PRODUCTION PO'I'IING 18 Claims, 7 Drawing Figs.

[52] U.S.Cl 248/19, 29/191.6, 156/293, 346/145 [51]" Int. 15/28 [50] Field of Search... 248/346;

16/(lnquired); 346/145; 156/293; 29/l91.6; 248/19 Primary ExaminerAllen B. Curtis Attorney-Christie, Parker and Hale ABSTRACT: A production process for equipping a rough casting with a plurality of highly accurate surfaces at precisely predetermined locations on the casting without machining the casting. The casting includes a plurality of laterally spaced holes and is placed on a tool which supports a plurality of mounting bosses in the holes of the casting. The tool locates the bosses generally coaxial with the holes so that annular spaces are provided between the exterior of the bosses and the walls of the holes, which spaces are then filled with a bonding agent to secure the bosses to the casting. The tool positions selected faces of the bosses in desired relation to each other, preferably parallel to a reference surface defined by the tool. The tool seals an end of each annular space to prevent the bonding agent from flowing from the space as the agent cures.

i 2 4001; 7 1' my fll Patented April 20, 1971 3 Sheets-Sheet l S R .0 v N E V N 1 PRECISION PRODUCTION POTTING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to a magnetic tape transport in which a rough casting is provided with a plurality of precision reference surfaces and holes and, more particularly, to a baseplate wherein a plurality of detail structural features are precisely positioned by inserts in apertures in a relatively rough casting.

2. State of the Prior Art Tape transports for use in digital data processing systems are highly precise mechanisms. Such precision is required so that a given reel of magnetic recording tape may be used with absolute interchangeability in any one of a number of instruments in the system. It is not at all uncommon, particularly in modern industrial and research enterprises as well as in business enterprises of a less technelogically oriented nature, that information is recorded onto a reel of magnetic recording tape at one location and read from the tape by different apparatus at a geographically different location.

Modern recording techniques feature high information packing densities and multiple, closely spaced recording tracks on a common strip of recording tape. In order that the tape may be used with the desired interchangeability in any number of tape handling transports which may be widely separated in geography, it is necessary that the transports be as identical as possible. Otherwise, information recorded by use of one tape transport may be inaccurately read from the tape on a different transport. Accordingly, tape transports for use in digital and analog data recording systems must be very precise instruments. The precision required in a tape transport is particularly significant with respect to the location and posi tioning of record and read heads, to the tape supply and tape takeup reels, and to the tape drive mechanisms.

In the past, magnetic tape transports have utilized heavy base castings, the castings necessarily being heavy to render the performance of the transport as uniform as possible notwithstanding variations in temperature and humidity of the surrounding atmosphere. According to prior manufacturing techniques, it has been the practice to machine into the casting desired holes and surfaces by which other elements of the transport are secured to the casting, such other elements typically including the reading and writing transducers and the tape transport drive motors. It is extremely difficult, however, to produce a precisely machined casting at low cost by use of the techniques heretofore relied upon.

it is well known, particularly in castings which have some portion substantially thicker than other portions, that internal stresses develop in the casting as the material of the casting cools. These locked-in stresses cause severe problems in precisely machining the casting. In the machining process. removal of the skin of the casting releases some portion of the stresses locked into the casting and causes the casting to distort. If a surface or hole being machined into the casting is to be precisely positioned relative to another hole or surface deformation of the casting during and as a result of the machining process interferes with the desired precision positional relationship. Accordingly, it is necessary in precision machining a casting to first heat treat the casting to remove as many of the locked-in stresses as possible, and then to exercise great care in machining the casting to prevent the generation of further stresses within the casting. If very precise dimensional relations are to be obtained in the final machined part, it is often necessary to subject the casting to repeated heat treatment and partial machining processes until the final machining process has been completed. Even then, it is common that the last stage of the fabrication process involve hand finishing operations upon the casting. Each step in the fabrica tion process entails a detailed inspection. Obviously, therefore, precision machining of castings, such as cast baseplates of magnetic tape transports, is an expensive and time consuming process.

This invention provides a manufacturing technique whereby baseplates for magnetic tape transports, for example, may be provided inexpensively and rapidly by personnel of relatively moderate skill. The precision obtained in the practice of this invention is at least as great, and can be far greater than, that obtained by adherence to techniques previously followed.

SUMMARY OF THE INVENTION Generally speaking, this invention provides a method of fitting a rough casting with a plurality of detail structural features at precisely predetermined locations relative to each other on the casting. The casting defines a plurality of holes and recesses at locations corresponding generally to the predetermined locations of the detail features. The method includes the step of providing a tool having a dimensionally stable base and defining a reference surface. A plurality of fixtures are mounted on the reference surface and are arranged in the predetermined relation to each other. The fixtures are configured to receive and to position selected bushings or mounting bosses, defining the desired detail features in a precisely predetermined arrangement corresponding to the arrangement of the predetermined locations of the detail features desired in the finished part. The casting is placed on the tool reference surface so that the fittings are aligned with corresponding ones of the holes and recesses in the casting. Selected bushings and bosses are positioned on the fittings to form the precisely predetermined arrangement. The positioning of the bushings and bosses on the fittings is accomplished so that they cooperate with the holes and recesses in the casting to define annular openings between them and the casting. The method also includes filling the annular openings with a hard curing bonding agent and curing the bonding agent sufficiently to secure the bushings and bosses to the castings in the predetermined arrangement before removing the casting and the bonded bushings and bosses from the tool.

The bushings which are bonded in the casting define either mounting apertures or the like for additional structural elements to be secured to the casting, or they define reference flats, shoulders and the like by which means additional elements are mounted to the casting. Preferably the bonding agent used to secure the bushings to the casting incorporates the same or a similar material as that which the casting and the bushings are made of, it being preferred that the bushings be manufactured of a hard or hardenable material to withstand wear during replacement of parts on the casting. Accordingly, after performance of the method reviewed above, the casting incorporates the machined bushings in an essentially integral manner and the resulting composite structure is the full equivalent of a casting which has been machined to have the same structural features as the composite structure. The composite structure is provided rapidly and inexpensively.

Preferably, the tool used in the procedure outline above has a major portion thereof defined of granite or the like to have extreme dimensional stability.

BRIEF DESCRIPTION OF THE DRAWINGS The above mentioned and other features of the invention are more fully set forth in the following detailed description of presently preferred embodiments of the invention, which description is presented with reference to the accompanying drawings, wherein:

FIG. 1 is a plan view of a tool, with casting mounted thereon, used for practicing the method of this invention;

FIG. 2 is a fragmentary front elevational view, in section, taken along line 2-2 of FIG. 1;

FIG. 3 is a fragmentary front elevational view, in section, taken along line 3-3 of FIG. 1;

FIG. 4 is a front elevational view of a magnetic tape transport base provided with a precision plate, and fabricated in accordance with the present invention FIG. 5 is a side elevational view, with parts broken away, of the transport base shown in FIG. 4;

FIG. 6 is a fragmentary front elevational view, in section, taken along lines 6-6 of HO. 1; and

FIG. 7 is a cross section elevation view of a pair of castings fabricated by the present method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 4 and show a base 10 for a magnetic tape transport with reference to which the present invention is described. A magnetic tape transport is illustrative of a particular application of this invention and is referred to merely as a vehicle for explaining the invention. lt should be understood that this invention can be practiced with any member which is to be fitted with a plurality of precisely positioned detail structural 7 features. The accompanying drawings have been simplified for the purposes of cl arity and ready understanding. The transport base is actually considerably more complex than suggested by FIGS. 4 and 5, for example. It should be understood therefore that the features described below and illustrated occur or are used in other areas of the base, as adjacent base openings 26, for example.

The base is defined by a casting 12 having a web 14 and flanges 16 and 38 extending away from the web substantially transverse thereto in opposing directions adjacent the periphery of the web. A plurality of coplanar precision mounting surfaces 20 support a precision plate 22 which is secured to the casting by means of bolts 24. The web is provided with a pair of laterally spaced cutouts 26 through which drive motor shafts for the tape reels of the tape transport project. The precision plate 22 is preferably constructed of glass to provide dimensional stability and includes suitable cutouts 28 and 30 which receive transducers (not shown) and tape drive cap stans (not shown) of the transport.

Precision tape recorders, such as tape recorders used in conjunction with data processing equipment, require utmost precision and accuracy in positioning the precision plate 22, especially relative to the tape reel drive motors. The positions of mounting surfaces 20, therefore, must be exact. For example, in some applications the mounting surfaces must be coplanar with respect to each other within a maximum tolerance of no more than fifty millionths of an inch. If the mounting surfaces were machined on a metal casting, such accuracy is most difficult to achieve and maintain and represents a substantial portion of the cost of manufacture of base 10.

To reduce heretofore high manufacturing costs, casting 12 is provided with a plurality of laterally spaced holes 32 disposed in web 14, as shown in FIG. ll, which receive a plurality of preferably cylindrical mounting bushings 34, also known as bosses, having planar faces 36 (FIG. 3) which are substantially transverse to axes of the bosses and which define the precision mounting surfaces 20 of the casting. The bosses have diameters which are less than the diameters of the corresponding casting holes such that an annular gap 38 is produced intermediate the periphery of the bosses and walls 40 of the holes. These gaps are filled with a bonding agent 42 which rigidly secures the bosses to the web of the casting 12. The faces 36 of the bosses are accurately positioned relative to the base casting in a common plane by a plurality of fixtures 43 mounted on a tool 44.

The bosses are low cost, mass-produced screw machine parts which are adapted to fit their particular application. Thus, they can be provided with an aperture 45, which can be threaded to engage a threaded bolt (not shown), or it may be manufactured smooth to receive a shaft (not shown). Altematively, the aperture can have another configuration or the boss can be solid (not shown) to serve merely as a shoulder on the finished base 30.

Referring now to FlGS. -3, the tool 44 is shown to comprise a baseplate 46 which defines a flat reference plane 48 and which is constructed of a material which affords dimensional stability under temperature variations. Preferably, the tool baseplate is constructed of a commercially available granite block which is precision ground to provide the flat plane. Each of a plurality of base holding clamp assemblies 50 includes a support post 52 which pivotally mounts a holding plate 54. A thumb screw 56 extends through a slot 58 in the holding plate and permits the holding plate to be tightened against flange 18 of transport base 10 when the transport base is disposed on the flat reference plane of the tool. The edge surfaces 57 of the transport base flanges are ground planar and parallel to each other; such a grinding operation can be performed readily and economically to the desired degree of precision on a Blanchard grinder, for example.

A plurality of pedestals 60 are secured to the flat plane 48 of the tool base to define portions of fittings 43. Preferably, the pedestals are made of meehanite for dimensional stability. The pedestals are arranged on the baseplate 46 such that one pedestal is disposed adjacent each hole 32 of the'transport base which is to receive a mounting boss 34. The distance between plane 48 and a face 62, defining the end of the pedestal remote from the tool base, is maintained with exactness to position the faces of the pedestals coplanar relative to each other or in some other desired precise relation. The pedestals further define upwardly open, internally threaded holes 64 for receiving bolts 66 disposed in axial apertures 45 of the cylindrical mounting bosses 34 to secure the bosses to the pedestals so that each boss face 36 is abutted against the adjacent pedestal face 62.

In a preferred embodiment of this invention, the pedestals include a relatively wide foot 70, a face of which proximate plane 48 is pennanently and securely bonded to the plane, and a cylindrical portion 72 adjacent the end of the pedestal defining face 62. Disposed about the cylindrical portion and supported by the foot of the pedestal is a helical compression spring 74, a substantially circular and flexible washer 76 made of silicone rubber sheet, for example, and a spongy buffer 78. The buffer has a configuration similar to that of the washer, and is disposed intermediate the washer and the end of the spring remote from the foot of the pedestal. The spring thereby biases the washer and the buffer away from baseplate 46 and toward web 14 of casting 12.

In another embodiment of the present invention, shown in FIG. 2, the cylindrical mounting boss 34 includes a flange 80 which defines the face 36 of the boss which is to be accurately positioned and which defines the detail feature to be imparted to casting 12. In this embodiment, the fitting can be a block 82 projecting away from tool reference plane 48 and defining a positioning surface 84 which mates with face 36 of boss flange 80. The block mounts an arbor 86, preferably of the expanding type, which extends normal to plane 48 and engages the axial aperture 45 in the boss to precisely locate the boss on the mounting block 82. The arbors may be used to advantage where the axis of boss aperture 45 is to be located with precision. Adjacent the periphery of flange 80 is a flexible annular washer 88 and an annular buffer 90 constructed of a spongy and flexible material such as polyurethane foam. The washer has an inner diameter slightly less than the outer diameter of the flange 80 and is biased in a direction away from block 82 by the buffer.

To fit the tape transport base with a plurality of precision mounting surfaces 20, the mounting bosses 34 are secured to the pedestals 60 by bolts 66, and to blocks 82 by expanding arbors 86, and surfaces 36 of the various bosses are tightly pressed against the respective pedestal surfaces 62 and 84. The transport base casting is placed on surface 48 of the tool such that the ground ends of flanges l6 engage the planar reference surface of the tool. The position of the casting is adjusted until all mounting bosses 34 are disposed in the corresponding holes 32 in web 14 substantially coaxial with the holes. Thereafter the clamping assembly thumb screws 56 are tightened to bias the holding plates 54 toward the ends of flanges 18 to substantially immovably secure the casting to the tool. The faces 36 of the mounting bosses are now accurately positioned with respect to each other since they are securely held against the positioning surfaces of the pedestals or the mounting blocks 60 or 82, respectively. Boss faces 36 define the detail structural features of interest, and these features are arranged in a precisely predetermined relation to each other.

Upon completion of the casting mounting procedure described above, washers 76 are biased towards the adjacent face 92 of casting web 14 by compression springs 74 or by spongy buffers 90. A seal is thereby established across the lower end of each annular space 38 from walls 40 of holes 32 to the periphery of the mounting bosses 34 adjacent the lower ends of the bosses. To prevent the transmission of excessive forces from the springs and bufiers to the web, which forces might deflect the web when it is secured to the baseplate by holding plates 54, and thereby counteract the advantages provided by the invention, the bias on each washer is kept as small as possible consistent with the requirement that the washer form a liquidtight seal between the adjacent boss and the casting. if the web of the casting is deflected as the casting is secured to the tool, the web will resume its undeflected state upon subsequent removal from the tool, thereby moving boss surfaces 36 out of the desired precisely predetermined relation defined by the tool, the bosses being securely bonded to the casting when the casting is removed from the tool.

After the casting has been positioned and clamped down on the tool, the bonding agent 42 is introduced into the annular gaps 38 between the bosses and the casting. The bonding agent is allowed to cure until it has hardened sufficiently to rigidly fix the bosses to the casting. Thereafter, the clamping assembly thumb screws are loosened and the casting is removed from tool 44. The faces 36 of the mounting bosses are aligned with an exactness which exactly reflects the precision of tool 44. The composite structure which is removed from the tool has the desired detail structural features thereof exactly related to each other according to a precisely predetermined arrangement.

The procedure described enables the manufacture of tape transport bases having precision mounting surfaces oriented with no appreciable tolerance variations in any one base or between different bases manufactured on the fixture. Manufacturing costs of the transport base are substantially less than when a casting is machined to provide it with precision mounting surfaces.

There are many commercially available bonding agents which can be utilized in the practice of the method of this invention. One bonding agent particularly well adapted for use in practicing this invention is sold under the trade name Devcon" and is manufactured by the Devcon Corporation of Danvers, Massachusetts. This bonding agent is a plastic metal" comprising approximately 80 percent of metal powder and percent of an extremely strong plastic resin. lt exhibits excellent adherence to metals, is nonvolatile, and does not shrink as it cures to a hardness comparable to that of metal. lf desired, the metal contained in the bonding agent may be the same metal of which the casting 12 is constructed so that the composite structure provided by the abovedescribed procedure has as uniform physical properties as possible. Also, the mounting bosses may be made of the same material as casting 112.

To strengthen the bond and prevent axial movements of a mounting boss relative to casting 12 because of insufficient adherence of the bonding agent to the mounting boss or the web of the casting, the holes 32 preferably are flared outwardly from the center of the hole toward each end as shown in both H08. 2 and 3, i.e., the holes have double draft. When an axial force is applied to the mounting boss, the hardened bonding agent is then mechanically restrained from breaking loose from the walls 40 of the holes 32. For the same reasons the peripheries of the mounting bosses are preferably provided with peripheral recesses 94 which are filled by the bonding agent to mechanically prevent axial movements of the mounting boss 34 relative to the bonding agent 42 and the hole 32 in web 14.

Referring to FIGS. 1 and 6, the tool 44 is shown to include a precision lateral spacer plate 96 having a plurality of apertures 98 for receiving the peripheries of several mounting bosses 34 to accurately position the mounting bosses precisely laterally relative to each other. The sponge buffers and sealing washers are disposed between the spacer plate and the casting around the bosses engaged by the spacer plate. Use of the spacer plate makes it possible not only to accurately locate the mounting bosses in an axial direction, such function being accomplished by fixtures 43, but also to accurately locate them precisely relative to each other in directions parallel to surface 48. In applications where high lateral spacing accuracy is not required, the spacer plate need not be used.

As noted above, mounting bosses 34 are provided at more locations of transport base 10 than are shown in the drawings. Bosses are provided in the casting adjacent casting openings 26 for mounting the drive motors for the tape reels of the transport, and these bosses have coplanar surfaces 36 adjacent the rear face of the base casting. The reel drive motors are then screwed to the bosses, the aligned surfaces of the bosses defining reference mounting surfaces for the motors. These reference surfaces may be primary reference surfaces for the transport.

The manufacturing procedures described above locate detailed structural features of the tape transport base, for example, relative to one face of the base casting. it may be desirable, however, especially with reference to precision plate 22, to have a secondary reference plane associated with the other face of the casting in the finished or nearly finished transport. FIG. 7 illustrates how this invention may be used to provide a secondary reference plane located on the side of the casting opposite from the primary reference plane and having a precisely predetermined relation, such as exact parallelism, to the primary reference plane.

As shown in FIG. 7, a plurality of mounting bosses 34 are bonded to casting 12, by the procedure described above, ad jacent a large opening I01 formed in casting web 14. These bosses have end surfaces 36 which are disposed adjacent web rear surface 92 in coplanar relation to define a primary reference plane 100. A secondary casting 102 has a central portion 103 disposed in opening 101 to be adjacent front face 104 of the web of casting 12. The secondary casting has a peripheral flange 105 which extends laterally of opening 101 adjacent the rear face of casting 12. Both the peripheral flanges and the central portion of the secondary casting carry bonded-in-place, axially bored mounting bosses 34 having flat locating end faces 36'.

The bosses mounted in the secondary casting are assembled into this casting by a procedure in accord with that described above, it being understood that the secondary casting has its own tool similar to tool 44. Boss surfaces 36' are all disposed parallel to each other, those associated with the peripheral flanges of the secondary casting being coplanar and those associated with the central portion of the casting being coplanar, such planes being parallel to each other. It will be observed that all bosses 34 are located with reference to a front face 106 of the secondary casting. The secondary casting is inverted on its tool for location of bosses 34' therein. Those bosses 34' which are carried by the flange of the secondary casting are located laterally of each other in correspondence with the pattern of those bosses 34 lying adjacent opening 101 in casting 12.

After the bosses have been secured in the secondary casting, the casting is mated with casting 12 so that the secondary casting flange bosses mate with the corresponding bosses of the principal casting, and the two castings are secured together by bolts 107 engaged with the aligned mounting bosses. The result is a composite structure which has a primary reference plane adjacent the rear face of casting 12 and a precisely parallel secondary reference plane 108 adjacent the front face of casting 12, the secondary reference plane being defined by surfaces 36' of the bosses carried in the central portion of the secondary casting. The precision plate of the tape transport conveniently may be mounted to the secondary casting.

By the use of suitable mounting bosses and appropriately configured tools, substantially any desired detail structural features having precisely determined interrelations may be imparted to a casting without appreciable machining of the casting. The bosses can be produced rapidly and inexpensively with great precision on screw machines, turret lathes, and other machine tools. Tools like tool 44 can be reused an indefinite number of times for volume production purposes to produce inexpensive composite structures which are exact duplicates of each other. The time consuming and costly machining, inspection and heat treating procedures which are encountered in producing large precision machined castings by conventional techniques are avoided by practice of the production method described above.

The foregoing description has presented this invention in the context of the production manufacture of a major component of a tape transport merely for the purposes of example in furtherance of the explanation of a presently preferred embodiment of the invention. it should be understood that the method and apparatus described above can be used to ad vantage in the volume manufacture of different precision members and parts. it should also be understood that the apparatus and procedures described can be modified without departing from the scope of the invention. Accordingly, the foregoing is not to be taken as limiting the scope of the invention defined in the following claims.

We claim:

1. In a magnetic tape recording apparatus including a tape transport comprising a baseplate, the improvement wherein said baseplate is a built-up assembly which comprises a structural member, a plurality of mounting apertures in the structural member, an insert in each of the mounting apertures, each insert having at least one surface precisely positioned in predetermined relation to a surface on another insert, which surface has a position in the baseplate which is essentially independent of the precise position of the aperture in the baseplate, and a rigid filler in the space between the insert in each aperture and the walls of the respective aperture for rigidly fixing the insert within the aperture.

2. A magnetic tape recording apparatus according to claim 1 wherein the precisely positioned surfaces of a plurality of the inserts are in a single plane.

3. A magnetic tape recording apparatus according to claim 1 wherein a plurality of the inserts each define first and second ones of said precisely positioned surfaces, the first surfaces of said plurality of inserts are in a first common plane, and the second surfaces of said plurality of inserts are in a second common plane.

4. A magnetic tape recording apparatus according to claim 3 wherein said first and second planes are parallel to each other.

5. A magnetic tape recording apparatus according to claim 4 wherein the first plane is on one side of the baseplate structural member and the second plane is on the opposite side of the baseplate structural member.

6. A magnetic tape recording apparatus according to claim l further comprising:

a secondary structural member having dimensional stability and defining therein a first plurality of mounting apertures;

an insert in each of the first plurality of mounting apertures in the secondary structural member, each insert having at least one surface precisely positioned in relation to a surface on another insert in said first plurality of apertures and essentially independent of precise position of the aperture; and

a rigid filler in the space between the insert and the walls of the respective one of the first plurality of apertures in the secondary structural member for rigidly fixing the insert within the aperture; and

means for securing an insert fixed in the secondary structural member to an insert fixed in the first-mentioned structural member, the insert in the secondary structural member having at least one surface precisely positioned in relation to a surface on the insert in the first-mentioned structural member.

7. A magnetic tape recording apparatus according to claim 6 wherein the secondary structural member further comprises:

a secondary plurality of mounting apertures;

an insert fixed in each of the secondary plurality of mounting apertures, and wherein the precisely positioned surface of each of the inserts fixed in the first plurality of mounting apertures in the secondary structural member is in a first plane and the precisely positioned surface of each of the inserts in the second plurality of mounting apertures in the secondary structural member is in a second plane parallel to the first plane.

8. A magnetic tape recording apparatus according to claim 1 further comprising:

means for mechanically connecting the tiller to the structural member; and

means for mechanically connecting the filler to the insert.

9. A magnetic tape recording apparatus according to claim 1 wherein the baseplate structural member and the inserts therein are fabricated of metal, and the filler fixing the inserts to the structural member comprises a major portion of metal particles and a minor portion of hard curing plastic resin.

10. A magnetic tape recording apparatus according to claim 9 wherein the metals defining the baseplate structural member, the inserts, and said particles are defined by substantially similar metals.

11. A magnetic tape recording apparatus according to claim I wherein the inserts are each circumferentially recessed within the limits of the mounting apertures, and the mounting apertures are defined by double drafted holes formed through the baseplate structural member.

12. In a magnetic tape recording apparatus including a tape transport comprising a baseplate, the improvement wherein said baseplate comprises a relative roughly finished baseplate structural member, a plurality of mounting apertures in the structural member, a relatively accurately finished insert in each of the mounting apertures, and a rigid filler in the space between the insert in each aperture and the walls of the respective aperture for rigidly fixing the several inserts within the corresponding apertures of the structural member, each insert having defined thereon at least one accurately defined and located reference surface, the several inserts as fixed to the structural member having their reference surfaces positioned in predetermined relation to a reference surface on at least another one of the inserts without substantial regard for the locations of the inserts relative to the corresponding apertures.

13. in a magnetic tape recording apparatus including a tape transport comprising a baseplate, the tape transport being defined to manifest a specified degree of precision in the relative positions of other components of the transport secured to the baseplate, the improvement wherein said transport baseplate is a built-up assembly which comprises a relatively roughly finished baseplate structural member, a plurality of mounting apertures in the structural member, a relatively accurately finished insert in each of the mounting apertures, each aperture being sufficiently oversized relative to the insert disposed therein that the aperture defines only broadly the position of the insert relative to the structural member in the completed baseplate, a rigid filler in the space between the insert in each aperture and the walls of the respective aperture for rigidly fixing the several inserts within the corresponding apertures of the structural member, each insert having defined thereon at least one accurately defined and located reference surface, each insert as fixed to the structural member having its reference surfaces positioned in predetermined relation to a reference surface on at least another one of the inserts without substantial regard for the locations of the inserts relative to the corresponding apertures.

14. A magnetic tape recording apparatus according to claim 13 wherein the inserts define means for mounting other com- 17. A magnetic tape recording apparatus according to claim 13 wherein the baseplate structural member is defined by an essentially unmachined casting and the inserts are comprised of machined elements defining detail structural features of the transport baseplate.

18. A magnetic tape recording apparatus according to claim 17 wherein the inserts are each circumferentially recessed within the limits of the mounting apertures, and the mounting apertures are defined by double drafted holes formed through the baseplate structural member. 

1. In a magnetic tape recording apparatus including a tape transport comprising a baseplate, the improvement wherein said baseplate is a built-up assembly which comprises a structural member, a plurality of mounting apertures in the structural member, an insert in each of the mounting apertures, each insert having at least one surface precisely positioned in predetermined relation to a surface on another insert, which surface has a position in the baseplate which is essentially independent of the precise position of the aperture in the baseplate, and a rigid filler in the space between the insert in each aperture and the walls of the respective aperture for rigidly fixing the insert within the aperture.
 2. A magnetic tape recording apparatus according to claim 1 wherein the precisely positioned surfaces of a plurality of the inserts are in a single plane.
 3. A magnetic tape recording apparatus according to claim 1 wherein a plurality of the inserts each define first and second ones of said precisely positioned surfaces, the first surfaces of said plurality of inserts are in a first common plane, and the second surfaces of said plurality of inserts are in a second common plane.
 4. A magnetic tape recording apparatus according to claim 3 wherein said first and second planes are parallel to each other.
 5. A magnetic tape recording apparatus according to claim 4 wherein the first plane is on one side of the baseplate structural member and the second plane is on the opposite side of the baseplate structural member.
 6. A magnetic tape recording apparatus according to claim 1 further comprising: a secondary structural member having dimensional stability and defining therein a first plurality of mounting apertures; an insert in each of the first plurality of mounting apertures in the secondary structural member, each insert having at least one surface precisely positioned in relation to a surface on another insert in said first plurality of apertures and essentially independent of precise position of the aperture; and a rigid filler in the space between the insert and the walls of the respective one of the first plurality of apertures in the secondary structural member for rigidly fixing the insert within the aperture; and means for securing an insert fixed in the secondary structural member to an insert fixed in the first-mentioned structural member, the insert in the secondary structural member having at least one surface precisely positioned in relation to a surface on the insert in the first-mentioned structural member.
 7. A magnetic tape recording apparatus according to claim 6 wherein the secondary structural member further comprises: a secondary plurality of mounting apertures; an insert fixed in each of the secondary plurality of mounting apertures, and wherein the precisely positioned surface of each of the inserts fixed in the first plurality of mounting apertures in the secondary structural member is in a first plane and the precisely positioned surface of each of the inserts in the second plurality of mounting apertures in the secondary structural member is in a second plane parallel to the first plane.
 8. A magnetic tape recording apparatus according to claim 1 further comprising: means for mechanically connecting the filler to the structural member; and means for mechanically connecting the filler to the insert.
 9. A magnetic tape recording apparatus according to claim 1 wherein the baseplate structural member and the inserts therein are fabricated of metal, and the filler fixing the inserts to the structural member comprises a major portion of metal particles and a minor portion of hard curing plastic resin.
 10. A magnetic tape recording apparatus according to claim 9 wherein the metals defining the baseplate structural member, the inserts, and said particles are defined by substantially similar metals.
 11. A magnetic tape recording apparatus according to claim 1 wherein the inserts are each circumferentially recessed within the limits of the mounting apertures, and the mounting apertures are defined by double drafted holes formed through the baseplate structural member.
 12. In a magnetic tape recording apparatus including a tape transport comprising a baseplate, the improvement wherein said baseplate comprises a relative roughly finished baseplate structural member, a plurality of mounting apertures in the structural member, a relatively accurately finished insert in each of the mounting apertures, and a rigid filler in the space between the insert in each aperture and the walls of the respective aperture for rigidly fixing the several inserts within the corresponding apertures of the structural member, each insert having defined thereon at least one accurately defined and located reference surface, the several inserts as fixed to the structural member having their reference surfaces positioned in predetermined relation to a reference surface on at least another one of the inserts without substantial regard for the locations of the inserts relative to the corresponding apertures.
 13. In a magnetic tape recording apparatus including a tape transport comprising a baseplate, the tape transport being defined to manifest a specified degree of precision in the relative positions of other components of the transport secured to the baseplate, the improvement wherein said transport baseplate is a built-up assembly which comprises a relatively roughly finished baseplate structural member, a plurality of mounting apertures in the structural member, a relatively accurately finished insert in each of the mounting apertures, each aperture being sufficiently oversized relative to the insert disposed therein that the aperture defines only broadly the position of the insert relative to the structural member in the completed baseplate, a rigid filler in the space between the insert in each aperture and the walls of the respective aperture for rigidly fixing the several inserts within the corresponding apertures of the structural member, each insert having defined thereon at least one accurately defined and located reference surface, each insert as fixed to the structural member having its reference surfaces positioned in predetermined relation to a reference surface on at least another one of the inserts without substantial regard for the locations of the inserts relative to the corresponding apertures.
 14. A magnetic tape recording apparatus according to claim 13 wherein the inserts define means for mounting other components of the transport to the transport baseplate with said specified degree of positional precision.
 15. A magnetic tape recording according to claim 13 wherein the baseplate structural member and the inserts are fabricated of metal, and the filler fixing the inserts to the structural member comprises a major portion of metal particles and a minor portion of hard curing plastic resin.
 16. A magnetic tape recording apparatus according to claim 15 wherein the metals defining the baseplate structural member, the inserts, and said filler particles are defined by substantially similar metals.
 17. A magnetic tape recording apparatus according to claim 13 wherein the baseplate structural member is defined by an essentially unmachined casting and the inserts are comprised of machined elements defining detail structural features of the transport baseplate.
 18. A magnetic tape recording apparatus according to claim 17 wherein the inserts are each circumferentially recessed within the limits of the mounting apertures, and the mounting apertures are defined by double drafted holes formed through the baseplate structural member. 